Process for producing metals and metal alloys low in carbon



Patented Mar. 14, 1933 mun GII'S'JI'QLI TOBVALD GUB'ILI'SSON, Q1 STOCKHOIM, SWEDEN PBOCEQS 1'02 PBDDUOING METALS AND METAL ALLOYS LOW IN CARBON Io Drawing. Application filed February 10, 1980, Serial No. 427,429, and in-lsweden February 19, 1988.

My present invention relates to improve; ments in processes for producing low carbon metals and metal alloys, for instance iron with a carbon content below 0.05%, so called 5 rustless iron and steel and other irons'and steels alloyed with carbon-binding metal or metals, e. g. chromium, man anese, tungsten, titanium and vanadium, an ferro-alloys of one or more of these metals, whereby a more complete utilization of the metal oxide or oxides contained in the employed ore or ores will be obtained than in the processes heretofore used.

A method has been developed for prpducing, for instance iron and steel allo ed with chromium, e. g. rustless iron, direct y out of iron ore and chromium ore. According to this method the finely divided ores are mixed with reducing agent, consisting of coal in a finely divided state, if desired in part replaced by thermic reducing agent of known t pe, whereat, however, the quantity of reuc1ng agent is kept less than the amount theoretically required for complete reduction of the ores. The mixture is then transformed into briquettes and the briquettes areldried or in any other way hardened and thereafter successively supplied into an electric furnace with one or more downwardl rected electrodes capable of being raise and lowered, and reduced and melted while swimming or lying in a relatively thin layer on r the slag bath in the furnace. Aftera suitable quantity ofcharge has been smelted, there are in the furnace an iron or steel bath comparatively rich in chromium and with a carbon content depending upon how great the deficit of reducing nt is kept in the briquettes and also upon t e operation of the furnace, and a slag rich in chromium oxide and ferrous oxide. From-this'slag part of the chromium and the iron is then extracted by adding ferro-silicon or the like to the sla in presence of the metal in the furnace use The chromium content in the iron or steel is in. this manner increased to the de e required for rustless iron or steel, an at the same time a "slag is obtained. that is more suitable for the ta ping.

5 "5. It has prove however, that) in this manchromium content in the slag is reduced, the

' spects.

have been supplied and melted separately in ner only a minor part of the content of iron and, above all, of chromium will be utilized. I Already after an addition of ferro-silicon in such a quantity that not quite one third of the silicon content in the metal, i. e. the iron or steel, will namely become so high that it in- I fluences considerably the roperties 0f the metal both in physical an in chemical re- Usually a percentage of silicon as low as possible will be desired in the rustless iron; it shall preferably not exceed 0.20 to For other irons and steels, however, other limits of .the suitable silicon content may exist, dependin amongother upon the 65 purpose for which t e product will be used.

When producing rustless iron with 0.10% carbon and about 13% chromium accordin to the method described above, the slag 'wi still contain 12 to 18% chromium oxide. and 4 to 8% ferrous oxide. On account of the high content of gangue in the chromium ores, the slag quantity will as a rule be very large or about 1.3 times the weight of the metal obtained, and thus the loss of chromium, especially, will be very important, amounting to about 40 to of the quantity of chromium supplied to the furnace as ore.

- Also in other known methods of producing rustless iron and steel wherein chromium ore is reduced and melted by thermic reducing agent, for instance aluminium, ferro-silicon orthe like, on or in a slag bath or on or in a steel bath in'an electric furnace or an openhearth furnace, it has proved, that the losses of chromium in the slag have been im ortant,v though the slag quantit has there y been i kept comparatively smal This has been the case whether the ore and the reducing agent arbitrary order or in admixture, and in thelatter case whether the charge has been in loose or in briquetted state. Also here the cause has been that the reducin a out has been supplied in a considerable elicit in order to cop the content of reducin agent,

for instance silicon, in the metal within allowable limits. When usin silicon exclusively as reduc ng agent, it as-also proved that, though a certain tested suitable deficit and vanadium ores, a high percentage of these metals will be obtained as oxides in the slag formed, even when the reducing agent is used in a quantity corresponding to or tosome degree exceedm the amount required for a complete reduction of the ore or ores, respective y. The same will bethe case if the production is carried out by melting a charge already reduced, consisting, for instance, of briquettes or a loose mixture of the raw materials which have been wholly or partly reduced in a special furnace or in a separate chamber of the melting furnace while using reducing agent in deficit or in a quantity approximately. corresponding to the amount re uired for complete reduction, or if such a c arge with reducing agent in 'exce ss is melted together with ore or. ores or a charge containin reducing a ent in deficit additionally supp ied to the urnace. The slag formed'in melting will thus also be rich in oxides of diflicultly reduced metal.

utilization of the' metal content of the ores used, above all of metal diflicultly reduced, will be attained than in the processes above described, whereby the cost of the'production of the low carbon metal or alloy, which is the princi a1 product inthe process, will be considera ly ecreased.

The main object of my resent invention is to utilize more complete y .and.suitably the,

slag rich in metal oxides obtained inreduction and/or melting processes of the kind mentioned above or of any similar kind, and

f. Another object thus, to render the process as a whole more economical."

of my invention is .to utilize .the content of metaloxides ins'aid sla in such a. manner that jag greater yield 0 "y, the prmci alprodz .low carbon metal or,

uct,'is obtained inthe process as a w ole than heretofore.

i amount of the employed reducing agent, and

In order to attain this, the slag rich metaloxides is according to the present in vention treated in two stages, which consist in, fi'r st adding tothe slag in the resence'of thelow carbon metal, already 'p mic reducing agent in such a quantity that the resulting metal below the slag contains an inconsiderable, or the properties of sai metal not substantially influencing,

second separating said metal and the slag thus pre-treated and thereafter adding to the slag more reducing agent, thermic f or carbonaceous, in such a quantity that a metal rich used in the concluding.e

uced, therin said latter reducing agent is obtained fromremaining metal oxide or oxides in the slag.

In both stages of the treatment heat should be supplied to the furnace used if required for carrying out the process.

The thermic reducing agent consists suitably of silicon, aluminium, calcium or alloys of one or more of these elements and ing of the charge for the low'carbon product is carried out. Most suited to this treatment are electric furnaces, especially furnaces with electrodes directed a inst the bath and capable of being raise and lowered, in which furnaces the heat, at least in part, is develin the slag so that the-temperature ofthe" slag may easily be controlled by regulating the resistance' heat in relation to the total heat developed in the furnace. The invention is, By the present invention a more effective;

used, for instance electric induction furnaces 'or o n-hearth furnacesr I low carbon thermic reducing agent is reatment the lining of the furnace should carbon free materials, so that carbon cannot be taken up'from the same b .the metal re-' duced out of the slag. For t e same reason 7 the heating of the sla should during the reduction preferably ta e place with the electrodes out of contact with the sla and the reducing agent lying on the-slag an elec tric furnace with carbon ,electrodes .is used for the treatment. If carbonaceous mate built of practicallyoped-in the form of electric resistance heat ably, successively in small portions. If the v reducing-agent is in, an unmolten' state it may preferably be added in finely divided form "and be spread over as large a portion ofthe slag surface as possible. Durmgthe' treatment the slag should be stirred, on one or moreoccasions in order to facilitate the reaction between the reducing agent afidthe metal oxides in the slag. If required for obtaining a'composition of the slag more suited to the furnace lining, or for making the slag more fluid so that'it will react more readily with the reducing agent and the reduced metal will better separate from the slag, suitably such slag forming materials, basic or acid, depending upon the composition of the lining, for instance lime, dolomite, clay, quartz or sand, may-be added to the slag either simultaneously with or after the reducing agent, as will form a suitable slag with the original slag and the reaction prodin form of metal oxides is reduced out of the' slag on account of the reducing agent being preferably supplied in a certain excess, the magnitude of which depends upon the percentage desired of the reducing agent in the metal produced at this stage. The slag will after this concluding treatment contain a very small quantity of metaloxides as comparedwith the slag before the pre-treatment, and,

thus, the loss of metal in the slag in the process as a whole will be only insignificant as compared with the losses in the methods hitherto used. This will especially be the case if the quantity of reducing agent in the after-treatment is adapted in such a way that the metal thereby produced contains 10% or more of reducing agent, for instance silicon. However, even if the metal containsonly .3 to 5% of reducing agent the utilization will be good. Naturally, lower percentages mav also be used. It is evident that the higher the percentage of the reducing agent is kept in the metal, the more completely will the content of metal oxides in the slag be won in the form of metal.

The'product rich in reducing agent obtained in the after-treatment of the sla which product will as a rule have a hig percentage of valuable, difficulty reduced metal, for instance chromium or manganese,

and thus will ofhigh value per unit of,

weight, may either be used for known purposes, tor. instance the form of ferrochrommm Hell n carbon, if carbonaceous reducing material 1s used in the after-treat- .ment, or be returned to the process. The

latter is'e'specially the case when thermic reducingagent low carbon is used. The practically carbon-free metal obtained in such a case in the after-treatment may thus ,suitablybeused in the pre-treatmentof the slag,as firstlythe content of reducing agent -in the metalwill be utilized for reducin of fresh metal oxides'out'of a new quantitp d a re .uce

slag, and secondly its content 0 metal bath present in thefurnace during the pre-treatment. The percentage of valu-- able metal, for instance chromium or manganese,- in the metal bath willhereby be mcreased essentially. Instead of obtaining a metal with about; 13% chromium in the directproduction of rustless iron according to the example previously mentioned, there will accordin to the present method be obtained from't -e same quantities of chromite and iron ore, firstly a somewhat greater yield, and secondly about 19% chromium in the metal. If a rustless iron or steel with about 13% chromium should be produced as final product a considerably smaller quantity of chromite can be used in the primary charge than in the unmodified direct process.

The metal rich in'reducing agent obtained .in the after-treatment of the slag may also be used as addition in the furnace for the production of the'prin'cipal roduct either alone or together with the c arge or as an ingredient of the same. If a briquetted charge is used the metal may thus be admixed in finely divided state with the mixture for preparing thebriquettes. 'Of metal rich in carbon, however, only a relatively small quantity can be added if the percentage of carbon in the product shall not be too high. In using metal low in carbon, the reducing agent in same will be utilized in the practically carbon-free metals will join the reductionprocess and can thus, if desired,

be used in its entirety at'this stage of the process. However, it is as a rule preferable to use the metal as addition, either alone or together with other reducing agent, for instance ferro-silicon if the metalcontains sili-.

con, in the pre-treatment of theslags The advantages of thepresent method for roducing low carbon metals and metal aloys' are, thus, that the reduction-and/or melting-process proper. 'for producing the principal product may be carried out without paying any great regard to the loss of valuable metal in the form of oxides in the slag, since yet the greatest possible part of said fnetal oxides will'be utilized in the pri'n cipal product proper without theproperties of the product being influenced substantially by the reducing agent used,"and the metal oxides thereafter remaining in the slag will also ,be utilized eflectively. In the special case when the product rich in reducing agent is returned to the process the metal ofthese remaining oxides will alsobe introduced into the principal product proper.

The invention is not limited to the metals" or materials which have here'inbefore been mentioned by way: of example only, but domprises any productior'iiof metals and metal alloys low in carbon or relatively low in car-- bon with theuse of the method set forth.

What I claim as new and desire to secure by Letters Patent of the United States of America is A 1. A process for producing metals and metal alloys low in carbon, consisting in re- 5 ducing and melting a charge containm oxide ore and reducing agent in deficit 0% the amount theoretically required for complete reduction of the metal oxides in the ore, treating the thereby formed s1 in constituents of reducing character, with thermic reducing agent in such a quantity as to obi'ain below the slag a metal bath containing said reducing .a ent onl in a pro- '15 portion insufiicient to su stantial 'y influence V for complete reduction of the metal oxides in from remaining metal oxidein the s ag.

- metal. produced se ratin and treating the all? th to obtain a meta the properties of the metal produced, se arating metal and slag,and treating the s kg with reducing agent, in such a quantity as to pbtain a metal rich in said reducin agent 2.- A rocess for producing metals and metal al oys low in carbon, consisting in reducing and melting a charge containing oxide ore and carbonaceous reducing agent in 25 deficit of the amount theoretically required for complee'reduction of the metal oxides in the ore, treatin the thereby formed slag rich in metal oxi e in presence of the low carbon metal thereby roduced with thermic. reducing agent in sue a quantity as to obtain below the slag a metal bath containing reducing agent in a proportion insuflicien't to substantially influence the properties of the metal and slag, g wi reducing agent in such a quantity as to obtain a metal rich in said reducing agent from remaining metal oxide in the ore. I i i 3. A recess for producing metals and 40 metal al oys low in carbon, consisting in reducing and meltin a chargecontain mg oxide ore of a readify oxidizable heavy metal and reducing a ent including carbonaceous material, the re ucingagent 1n deficit of the amount theoretically required for complete reduction of the metal oxides in the ore, treating the thereb formed slag bath rich in oxide of said readi y oxidizable heavy metal,

iii {presence of the produced metal bath poor int/constituents of reducing character, with thermic reducing a ent in such a quantity as to'obtain below t e slag a metal bath containing reducing agent in aproportion insuflicient to substantially influence the properties of the metal produced, separating meta1 and slag, and treating-the slag with thermic reducing agent in such .a quantity .as

rich in said reducing agent a from remaining metal oxide in the slag.

ducing'and melting a charge containing oxide ore and carbonaceous reduemg agent in deficit of the amount theoretically required I rich in metal, 1 oxide, in presence of the pro uced metal poor .4.A process for producing metals and metal alloys low in carbon, consisting rethe ore, treating the thereby-formed slag rich in metal oxide, in presence of the low carbon metal thereby produced, with siliceous thermic reduc agent in such a quantity as to obtain below t e slag a metal bath containing silicon in a proportion insuflicient to substantially influence the properties of the metal produced, separating metal and slag,

and treating the slag with siliceous therm1c reducing a ent in such a quantity as to obtain a metal ric in silicon from remaining metal oxide in the slag.

5. In a process ior roducing metals and metal allo slow in car on wherein a low carbon metal iferouschar e containinga readil oxidizable heavy metal is melted, under 0x1- dizing conditions, thereby forming a low carbon metal bath and a sla bath rich in oxide of said readily oxidiza le metal, the

s stepsof treating said slag bath in presence of said metal bath with thermic reducing agent in such a quantity as to. obtain below the slag a metal bath containing reducing agent in a proportion insufiicient to substantiall influence the properties of the metal pr uced, separating metal and slag, treatmg the slag with thermic reducing agent in such a uantity as to obtain/ametal rich in said reducing agent from remainin metal oxide in the slag, and further utilizin the contents of reducing agent and. of r uced metals in said latter metal by adding the metal to a new quantity of slag, rich in metal oxide and produced in the process, in the first treatment of said slag. I

6. A, rocessfor producing metals. and

metal al 03's low in carbon, consisting in reducin an melting a charge containing oxide ore o a carbon-binding metal and reducing agent in deficit of the amount theoretically re uired for complete reduction of the metal oxides in the ore, treating the thereby formed slag rich in metal oxide, in presence of the thereby produced metal poor in constituents of reducing character, with thermic reducing agent in such a quantity as to obtain below agent in-a proportion insufiicient to substant lall' influence the properties of the metal pr u'ced,separatin metal and slag, treatin the slag with therm c reducing agent in sue a quantity as to obtain a metal rich in said reducin agent from remaining-metal oxide,

the slag a metal bath containing reducing tion insuflicient to substantially influence the properties of the metal produced, separating reducing agent in such a quantity as to obtain a metal rich in said reducing agent from remaining metal oxide in the slag, and further utilizing the contents of reducing agent and of reduced metal in said latter'metal by-add-' ing the metal to a new oauantity of slag, rich 'in' metal oxide and pr need in the process, in the first treatment of same and to a new quantity of the primary charge. 8. A rocess for producing metals and metal al oys low in carbon, consisting in reducing the melting a charge, containing oxide ore of a carbon-binding metal and carbonaceous reducing agent in deficit of the amount theoretically uiredfor complete reduction of the metal oxldes in the ore, treating the thereby formed slag bath rich in metal oxide, in resence of the low carbon metal bath there y produced, with thermic reducing agent in such a quantity as to obtain below the slag a metal bath containing reducing agent in'a'proportion insuficient to substantially-influence the properties of the metal produced, separating metal and slag, treatmg the slag with thermic reducing agent in in said reducing agent from remaining metal oxide in the slag, using in both said stages of the treatment of the slag an electric furnace with a downwardly directed electrode capable 0 of being raisedand lowered, and s'upplyin V the electric heat r uired for the process wit the electrode out :2

with the reducing agent on the slag.

9. A process for producing metals and metal alloys low incarbon," consisting in smelting a charge containing oxide oreand thermic reducing agent, the latter in a quantity less than that theoretically required for complete reduction of the metal oxides in the ore, treating the thereby formed slag rich in metal oxide in presence of the low carbon metal thereb produced with thermic reducing agent 0 a stronger reducing character than that of the reducing agent used in the reduction of the ore, the reducing agent being added to. the slag in such a quantity as to obtain below the slag a metal bath containing reducing agent, in a proportion insuflicient to substantially influence the properties oi the metal produced, separating metal and slag, and treating the slag with reducing agent in such a uantity as to obtain a metalrich in said re, ucin agent from remaining metal oxide in thes a'g.

66 10. A process for producing metals metal and slag, treating the slag with thermic such a quantity as to obtain a metal rich contact with the slag and thermic reducing metal alloys low in carbon, consisting in reducing and meltingv a briguetted charge of intimately mixed finely divided oxide ore and finely divided reducing agent, the latter in a uantity less than that theoretically required or complete reduction of the metal oxides in the ore, on and in a slag bath in an electric furnace provided with a downwardl directed electrode capable of being raised an lowered, treating the thereby formed slag rich in metal .oxides in presence of the low carbon metalthereby produced with thermic reducing agent in such a quantity as to obtain below the slag a metal bath containing reducing agent in a proportion insuflicient to substantially influence the properties ofthe metal pr uced, separating metal and slag, treatin the slag with thermicreducin'g agent in such a quantity as to obtain a metal rich insaid reducing agent-from remaining metal 'oxide in the slag, and further utilizing the contents ofreducing agent and of reduced metals in said latter metal by adding the metal to a new quantity of slag from the melting of the charge in the first treatment of said slag.

11. A process for producing chromiumiron-alloys low in carbon, consisting in reducing and melting a charge containing chromium oxide, iron oxide and reducin agent, the latter in a quantity less than that t eoreti-.

cally required for complete reduction of the 4 metal oxides in the charge, treating the thereby formed slag bath rich in chromium oxide and ferrous oxide, in presence of the roduced metal bath poor in constituents o reducing character, with siliceous thermic reducing agent in such a quantity as to obtain below the slag a metal bath containing silicon in a proportion insuflicient to substantially influence theproperties of the chromiumiron-alloy produced, separating metal and slag, then treating the slag with siliceous thermic reducing agent in such a quantity as to obtain a chromium-iron-silicon-alloy rich in silicon from remaining metal oxides in the slag, and. further utilizing the contents of silicon and of chromium and iron in said latter alloy by adding same to anew quantity of slag, rich in chromium oxide and ferrous oxide and produced in the process,- inthe first treatment of said slag.

- 12. A processfor producing metals and metal alloys low in carbon, consisting in reducing a charge containing oxide ore of a carbon-binding metal incompletely so that a metallic product containing a considerable amount of reduced metal oxide is obtained,

melting said partly reduced product, thereby forming a low carbon metal bath and a slag bath rich in metal oxide, treatin said sl a bath in presence of said metal ath. wmt

ent in such a quantity as, to obtain below t e slag a metal bath containing reducing agent in a proportion in.- suflicient tosubsta'ntially influence the prop- 5 metal oxide in the slag.

erties of the metal produced separating metal and slag; and treating the siag with reducin agent in such a quantity as to obtain a meta rich in said reducing agent from remaining 13. A process for producing metals and metal alloys low in carbon, consistingin reducing a chargecontaining oxide ore of a' carbon-binding metal and reducing agent in deficit of the amount theoreticallyrequired for complete reduction of the metal oxides in J the ore, melting the metallic product thps obtained, thereby formin a metal bath poor in reducing agent and a a%bath rich in metal 5 oxide,- treating said slag ath in presence of said metal bath with thermic reducin agent in such a quantity as to obtain below t e slag a metalbath containing reducing a 'ent in a proportion insufiicient to substantia y influ- 20 ence the properties of the metal produced, separating metal and-slag, and treating the slag with reducing-agent in such a quantity as to obtain a metal rich in said reducing agent from remaining metal oxide in the slag. 25 In testimony whereof I aflix my si nature. ml. GUSTAF 'l'ORVAI-D GUST S5021. 

